We have an opportunity to show off a many-to-many relation in our sample app and I don't want to miss that. In a real-world scenario, only a limited quantity of a particular item belongs to a particular order. Imagine, you have an order cart containing references to some selected items with their respective ordered quantities. The end result is you got a relationship something like: an order can have many items whereas an item can be part of multiple orders.

By EF conventions, in a many-to-many relation, you have two standalone entities and a third entity between them which represents a relationship bridge. In our case, the bridging entity will be the OrderItem.